It is well known that oligosaccharides have various biological activities such as anticarcinogen, diagnostic reagent, physiologic activities, functional foods, cosmetics and so on. Chitosan oligosaccharides owned distinctly applying perspective against chitin and chitosan such as excellent solubility, no antigenicity, soft build-up effect in host, and so on. However, at present, because of complex prepare technique of chitosan oligosaccharides and dim action principle, their price is very expensive and their large-scale applications are confined. The reason of above-mentioned results is that the preparation technique and action mechanism of chitosan oligosaccharides not were deeply studied yet. Obviously, this result was not coincident with the abundant chitin resource in our country.
It is well known that chitosan oligosaccharides are mainly prepared by degradation of chitin and chitosan. At present, several methods have been suggested for the preparation of chitosan oligosaccharides such as acidic depolymerization, oxidative degradation, supersonic degradation and so on. However, the yield of chitosan oligomers that were degraded by above-mentioned methods was low (about 10˜50%). Moreover, molecular weight and yield of the resultant were unstable, that is a bad repeatability by using these methods. Because of low yield, a lot of chitosan was wasted and serious waste of raw material leaded to the higher cost of material. In order to decrease the cost and improve the yield of the resultant, ameliorated preparation technique has become a key problem.
Microwave irradiation technique, a new organic synthesis technique, replaces of the conventional heating methods to apply to organic dry or wet reaction in the late 1980S. Compared with the conventional heating, microwave irradiation has some distinct advantages such as fast reaction, high yield, uniform heat and uniform quality of the resultant. So the methods of microwave irradiation have large-scale application perspectives, for example, in Diels-Alder reaction and its annelation. The principle of microwave dielectric heating, described as “inside heating”, is ion migrate or polar molecule rotate makes the molecule motion. So it did not result in the change of inner molecular structure and it quite improved reaction rates and selectivity. Therefore, microwave heating was widely applied to organic dry and wet reaction. It pioneered a new road to some reactions that they are difficult to perform in the way of conventional heating and it made some inert substances become active. However, few people have studied the preparation of chitosan oligosaccharides under microwave irradiation, none on salt-assisted acid hydrolysis preparation under microwave irradiation.